JP2003188310A - Method of manufacturing circuit board with electrode terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a circuit board with electrode terminals having high insulation performances can be manufactured with improved productivity without using solder. <P>SOLUTION: To a ceramic substrate composed mainly of an aluminum nitride or a silicon nitride, (a) a copper circuit or a copper plate is bonded by using a brazing material containing silver, copper, tin, and zirconium and heating the brazing material under a nitrogen atmosphere or (b) an Al or Al-alloy circuit or an Al or Al-alloy plate is bonded by using at least one kind of bonding material selected from among Al-Cu-based alloy foil, powder of the Al-Cu-based alloy foil, and mixed powder containing Al and Cu and heating the bonding material under the nitrogen atmosphere. When the copper plate or the Al or Al-alloy plate are bonded to the ceramic substrate, the copper circuit or Al or Al-alloy circuit is formed by etching the plate. Thereafter, the electrode terminals are attached to a portion of the circuit having a ≤1/3 area of the circuit, area of each terminal being 3-30 mm<SP>2</SP>, by imparting ultrasonic energy to the terminals under a specific condition. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a circuit board with electrode terminals suitable for a power module. 2. Description of the Related Art In recent years, high-performance modules such as high-power and high-efficiency inverters have progressed with the advancement of the performance of industrial equipment such as robots and motors, and the heat generated from semiconductor elements has been increasing steadily. Following. In order to efficiently dissipate this heat, in a large power module substrate, a ceramic substrate mainly composed of aluminum nitride or silicon nitride (hereinafter, referred to as "aluminum nitride substrate") having good heat conduction and both front and rear surfaces thereof are used. After joining a copper plate and forming a copper circuit on one side by etching and a heat-dissipating copper plate on the other side, make a circuit board as it is or by performing processing such as plating, and make a semiconductor element and electrode terminals on the copper circuit part Is used by soldering a heat-dissipating copper plate on the opposite surface to a base copper plate and then attaching it to a heat sink. [0003] Since the solder used here contains lead, the use of lead-free solder is being studied from the viewpoint of today's environmental problems. On the other hand,
A joining method that does not use solder is also being studied, and welding of the electrode terminals using ultrasonic waves of 30 to 200 kHz has already been proposed (Japanese Patent Application Laid-Open No. 2000-232189). However, even with a circuit board with electrode terminals mounted under these ultrasonic conditions, insulation resistance varies greatly depending on the manufacturing history and circuit shape of the circuit board,
In some cases, breakdown occurred when AC 5000 V was applied for 3 minutes, or dielectric breakdown occurred at the beginning of the manufacturing process if repeated thermal cycles were performed at best. [0004] An object of the present invention is disclosed in Japanese Patent Laid-Open No. 2000-2321.
An object of the present invention is to solve the above-mentioned problem in JP-A-89-89, and to manufacture a circuit board with electrode terminals having high insulation resistance without using solder. An object of the present invention is to use a substrate such as aluminum nitride as a ceramic substrate and join a copper circuit using a brazing filler metal containing tin or join a circuit made of Al or an Al alloy using an Al-Cu-based joining material. This can be achieved by manufacturing a circuit board by applying ultrasonic waves of a specific condition to a specific upper surface of the circuit and attaching electrode terminals. [0005] That is, the present invention is as follows. (A) using a brazing material containing silver, copper, tin and zirconium on a ceramic substrate mainly composed of aluminum nitride or silicon nitride and heating it in a nitrogen atmosphere to join a copper circuit or a copper plate, or (b) Using Al-Cu alloy foil, powder of Al-Cu alloy foil, and at least one type of joining material selected from a mixed powder containing Al and Cu, the material is made of Al or an Al alloy by heating under a nitrogen atmosphere. After joining a circuit or a board, when a copper plate or a plate made of Al or an Al alloy is joined, etching is performed to form the circuit. 3-30mm mounting area for electrode terminals
² , at least one of the electrode terminals has an output of 300 W
As described above, a method of manufacturing a circuit board with electrode terminals, characterized by applying ultrasonic energy having a frequency of 7 kHz or more and an amplitude of 7 μm or more. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below. The feature of the present invention is that an electrode terminal is ultrasonically bonded to a circuit board manufactured under specific conditions under specific conditions. The ceramic substrate used in the present invention is a substrate such as aluminum nitride. As a material mainly composed of aluminum nitride, the strength and the thermal conductivity purity are 400 MPa.
As described above, it is preferably at least 150 W / mK and at least 93%, and as a material mainly composed of silicon nitride, the strength and the thermal conductivity purity are preferably at least 600 MPa, at least 50 W / mK and at least 93%. . Since these ceramic substrates are commercially available, they can be used. When the circuit metal and the heat dissipating metal are copper, the metal components of the brazing material are preferably 40 to 64% of silver, 12 to 28% of copper, 12 to 22% of tin, and 8 to 16% of zirconium. If the silver content is less than 40%, the amount of the intermetallic compound of copper and tin increases, the bonding layer becomes brittle, and the reliability of mechanical strength is greatly reduced. On the other hand, if it exceeds 64%, the wettability of the brazing material to the copper plate (or copper circuit or heat-dissipating copper plate) is reduced, and voids are formed in the bonding layer to lower the bonding strength. If the content of copper is less than 12%, the melting point of the brazing material is significantly increased, and the wettability of the brazing material is deteriorated. If it exceeds 28%, the amount of the intermetallic compound of copper and tin increases, the bonding layer becomes brittle, and the reliability of mechanical strength is greatly reduced. If the tin content is less than 12%, the brazing filler metal is easily oxidized, the melting point of the brazing filler metal rises, the joining temperature must be increased, and voids are formed in the joining layer to increase the joining strength. descend. On the other hand, if the content exceeds 22%, the amount of the intermetallic compound of copper and tin increases, the bonding layer becomes brittle, and the reliability of mechanical strength is greatly reduced. As the active metal, zirconium is selected. If the zirconium content is less than 8%, the bonding strength between the substrate such as aluminum nitride and the bonding layer is weak, and if it exceeds 16%, the bonding layer becomes brittle and the reliability of the mechanical strength decreases. In the present invention, the zirconium component diffuses into the substrate such as aluminum nitride, and the tin component improves the wettability of the silver component and the copper component on the copper plate (or copper circuit or heat-dissipating copper plate). Even if it is not, a substrate such as aluminum nitride and a copper plate (or a copper circuit or a heat dissipation copper plate) are firmly joined by firing in a nitrogen atmosphere. As the metal component of the brazing material, a foil or powder of such a simple substance or an alloy can be used as it is. Preferably, a paste is prepared, and the paste is mixed with a substrate such as aluminum nitride and a copper plate (or a copper circuit or a heat dissipation copper plate). And heat treatment. An example of the paste formulation is 4 to 10 parts of a medium such as polyisobutyl methacrylate (PIBMA) per 100 parts of the metal component. The application amount of the paste is preferably 9 to 10 mg / m ² on a dry basis. The paste is a substrate such as aluminum nitride and / or
Alternatively, it is applied to a copper plate (or a copper circuit or a heat dissipation copper plate). The copper plate (or copper circuit or heat-dissipating copper plate) used in the present invention is preferably an oxygen-free copper plate, particularly an oxygen-free copper plate having an oxygen content of 50 ppm or less, particularly 30 ppm or less. When a copper circuit pattern or a heat-dissipating copper plate pattern is joined, etching is not particularly necessary. However, when a copper plate is joined, etching is required to form a copper circuit or a heat-dissipating copper plate from the copper plate. This is because Al
The same applies to a case where a plate (aluminum plate) made of an Al alloy is joined. The thickness of the copper circuit is desirably 0.1 to 0.5 mm, and the thickness of the heat dissipation copper plate is desirably 0.1 to 0.5 mm. The circuit board manufactured by the present invention preferably has a bonding layer having a thickness of 8 to 13 μm. If the thickness of the bonding layer is less than 8 μm, the bonding becomes insufficient, and if it exceeds 13 μm, the amount of intermetallic compound of copper and tin increases, and the bonding layer becomes brittle. The thickness of the bonding layer is
It can be easily adjusted by the thickness of the brazing material. A laminate of a substrate such as aluminum nitride and a copper plate (or a copper circuit or a heat-dissipating copper plate) sandwiching a brazing material is subjected to pressure 1.
It is preferable to bake while pressing at 0 MPa or more.
If it is less than 1.0 MPa, the gap where the brazing material is exposed to the atmosphere becomes large, so that the joining becomes insufficient. The upper limit of the pressing force is not limited, but about 2 MPa is sufficient. The bonding atmosphere of the laminate is a nitrogen atmosphere.
Preferably, a nitrogen atmosphere having an oxygen concentration of 1 to 100 ppm is used. If the oxygen concentration exceeds 100 ppm, the brazing material will be oxidized and bonding will be insufficient. On the other hand, if the oxygen concentration is less than 1 ppm, the wettability of the brazing material is extremely improved, and the temperature control becomes difficult, which is not preferable. In addition, the cost of the product is not sufficiently reduced because the device becomes large. The bonding is performed at a temperature of 750-850 ° C. for 0.5-
Hold for 2 hours. If the temperature is lower than 750 ° C., the bonding is not sufficient. If the temperature exceeds 850 ° C., the diffusion of silver or tin into the copper plate (or the copper circuit or the heat dissipating copper plate) becomes excessive and the bonding layer becomes brittle. If the holding time in this temperature range is shorter than 0.5 hour, the bonding becomes insufficient, and if it is longer than 2 hours, the diffusion of silver or tin into the copper plate (or copper circuit or heat dissipation copper plate) becomes excessive. Then, the bonding layer becomes fragile. In the present invention, 750.degree.
The rate of temperature rise up to 750 ° C. and the rate of cooling from 750 ° C. to a take-out temperature such as room temperature are also important, and all are preferably 300 ° C./hour or more. If the rate of temperature rise is less than 300 ° C./hour, the brazing material will be oxidized and bonding will be insufficient. If the cooling rate is less than 300 ° C./hour, particularly in the temperature range of 600 ° C. or more, Ag or Sn in the brazing material layer
Such components diffuse to the copper plate (or copper circuit or heat-dissipating copper plate) side, and the reliability of the circuit board is reduced. Also, 600
If the cooling rate is reduced in a lower temperature range than ℃, the productivity will not be improved. Next, a case where the circuit metal and the heat dissipation metal are Al or an Al alloy (hereinafter, referred to as "aluminum") will be described. For details, see JP-A-2001-085
No. 808. As the joining material, Al
-Cu-based alloy foil, powder of Al-Cu-based alloy foil, and Al
At least one type of joining material selected from a mixed powder containing Cu and Cu is used. Among them, an Al—Cu alloy foil is preferable, and in particular, 1/10 to 1 with respect to the thickness of the aluminum circuit.
An alloy foil having a thickness of / 50 is preferred. If the thickness is less than 1/50, it is difficult to achieve sufficient bonding, and if it exceeds 1/10, the aluminum circuit becomes hard and disadvantageous to the thermal history of the circuit board. Particularly preferably, the thickness is 100 μm or less, and more preferably, 1/100 of the thickness of the aluminum circuit.
The thickness is 12 to 1/40. Usually, the thickness is 0.4-0.
Since an aluminum circuit of 6 mm is used, the thickness of the bonding material is 10 to 50 μm, particularly about 15 to 30 μm. As the aluminum plate (or aluminum circuit or heat-dissipating aluminum plate), 1000 series pure Al
Needless to say, a 4000-type Al-Si-based alloy or a 6000-type Al-Mg-Si-based alloy, which can be easily joined, can be used. Above all, high-purity Al having a low yield strength (purity of 99.85% or more) is preferable. Such an aluminum plate is commercially available as 1085, 1N85 material.
Also, 99.9% (3N) products and 99.99% (4N) products can be used because they are not so expensive. The aluminum circuit may be a single unit, or may be a laminate of two or three or more clads. Examples of the laminate include Al-Ni, Al-Ni-Cu, A
1-Mo, Al-W, Al-Cu and the like. They are,
It is appropriately selected according to the purpose of use and the joining method. Among them, it is preferable to use a rolled sheet of Al alone having a purity of 99.99% or more, particularly a rolled sheet having a rolling reduction of 10% or more. The reason why a rolled Al plate is preferable is that uniform plastic deformation is more likely to occur because uniform rolling is repeatedly performed with a roll as compared with the molten aluminum method. The higher the purity of aluminum in the aluminum circuit, the better, but it is expensive, so that a commonly available product of about 99.999% is suitable. The thickness of the aluminum circuit is usually 0.3 to 0.5 mm. If this range is remarkably deviated, the relationship with the preferable thickness of the bonding material cannot be maintained. For example, for an aluminum circuit having a thickness of 3 mm, the thickness is 200 μm, which is 1/15 of the thickness.
Does not have an appropriate thickness, and a hard layer disadvantageous to the heat history is formed. Further, in order to optimize the hardness of the aluminum circuit to generate plastic deformation relatively uniformly, to prevent plating and bonding wire from peeling, and to significantly reduce damage such as solder cracks, the thickness of the aluminum circuit is reduced. 1
Vickers hardness of 15 kgf / mm ²
The following is preferred. The heat radiation aluminum plate has a purity of 99.
It is sufficient if the thickness is 0% or more, and the thickness is 0.1 to 0.5 m.
m is desirable. The preferred composition of the bonding material is 86% or more of Al, 1 to 6% of Cu, and 3% or less of Mg (not including 0), particularly 0.2 to 2.0%. Further, Zn, In, M
5% in total of components such as n, Cr, Ti, Bi, B, and Fe
Degrees below can be included. With such a composition, the circuit board can be supplied more stably and at low cost. Specific examples of the joining material (commercially available alloy) are shown below.
2018 alloy, 2017 alloy, and JIS alloy 20
01, 2003, 2005, 2007, 2011, 20
14, 2024, 2025, 2030, 2034, 20
36, 2048, 2090, 2117, 2124, 22
18, 2224, 2324, 7050 and the like. The bonding atmosphere of the laminate is a nitrogen atmosphere, preferably a nitrogen atmosphere having an oxygen concentration of 1 to 100 ppm. The joining temperature is between 600 and 650 ° C. The ultrasonic bonding used in the present invention is performed by using an apparatus such as USW-610Z20S manufactured by Ultrasonic Industry Co., Ltd. and selecting the conditions. First, the output is 300
It is adjusted by the size of the circuit board and the electrode terminals in the range of W or more, preferably in the range of 500 to 2500 W.
If the output is less than 300 W, the bonding will not be sufficient. The frequency is 7 kHz or more, preferably 10 to 28 kHz.
When the frequency is lower than 7 kHz, the bonding is not sufficiently performed. When the frequency is higher than 28 kHz, the vibration becomes too large, and the bonding is not sufficient. The amplitude is 7 μm or more, preferably 10 to 100 μm. If the amplitude is less than 7 μm, the bonding will not be sufficient. Furthermore, the time for giving the vibration is preferably 0.5 to 5 seconds, particularly preferably 1 to 3 seconds. Since a metal conductive material serving as an electrode terminal is required to be inexpensive and have high electric conductivity, the circuit is made of a copper circuit,
Copper or copper alloy is preferred in any of the aluminum circuits. One example of the dimensions is a thickness of 0.5-1.
5 mm, width 2 to 2.5 mm. In the present invention, when the electrode terminals are mounted on the upper surface of the copper circuit or the aluminum circuit, the mounting area is an important condition. That is, 1/3 or less of the circuit on the area (the area on their total in the case of division circuit) (i.e. the mounting area ratio is less 33.3%) in the area of, moreover 3 to 30 mm ² the mounting area of one location It is to be. If more than one-third of the circuit area is mounted, it will be vibrated and peeled when another electrode terminal is mounted, making it impossible to mount a plurality of electrode terminals. A preferable mounting area ratio is 5 to 20%. Further, if one mounting area is smaller than 3 mm ^2, it is insufficient to satisfy the function as an electrode terminal, and if it is larger than 30 mm ² , it is difficult to perform ultrasonic welding. A preferable one attachment area is 4 to 8 mm ² . The electrode terminals are
Usually, a plurality is attached. EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. In addition, "%", "part" described in this specification
Are based on mass. Examples 1-3, 7-11 Comparative Examples 1-8 Silver powder (1.1 μm, 99.3%), copper powder (1.4 μm)
m, 99.8%), tin powder (5.0 μm, 99.9)
%) And zirconium powder (5.5 μm, 99.9%) in a ratio of 51.4 parts of silver, 20.0 parts of copper, 14.3 parts of tin, and 14.3 parts of zirconium. A terpineol solution was added and kneaded to prepare a brazing filler metal paste A containing 71.4% of a metal component. On the other hand, silver powder (1.1 μm, 99.3)
%), Copper powder (1.4 μm, 99.8%) and titanium hydride powder (5.0 μm, 99.9%) in a proportion of 80 parts silver, 15 parts copper, and 5 parts titanium hydride, A terpineol solution of polyisobutyl methacrylate was added and kneaded to prepare a brazing filler metal paste B containing 71.4% of a metal component. The brazing material paste was applied to an aluminum nitride substrate (size: 60 mm × 36 mm × 0.65 mm).
Flexural strength: 500 MPa Thermal conductivity: 155 W / mK,
(Purity: 95% or more) was applied to both surfaces by a roll coater. The coating amount at that time is 9 mg / cm on a dry basis.
^{And 2} . Next, a 56 mm × 32 mm × 0.3 mm oxygen-free copper plate (oxygen amount: 10 ppm) was placed on the copper circuit forming surface of the aluminum nitride substrate, and 56 mm × 32 mm × 0.3 mm was placed on the heat radiation copper plate forming surface.
mm x 32 mm x 0.15 mm oxygen-free copper plate (oxygen content:
10 ppm) and then joined under the joining conditions shown in Table 1. Then, a resist ink is screen-printed so as to form a circuit pattern of a predetermined shape on the copper circuit forming surface and a heat radiating plate pattern on the heat radiating copper plate forming surface. A circuit board was manufactured by performing P plating (thickness: 3 μm). In addition,
The oxygen concentration in the nitrogen atmosphere was 50 ppm.
In a vacuum of 1 × 10 ⁻³ Pa. Examples 4-6, 12-16 Comparative Examples 9-1
4 A on the front and back surfaces of the aluminum nitride substrate
The l-plates were stacked, sandwiched between CC composite plates (2 mm thick), and heated in a nitrogen atmosphere with an oxygen concentration of 50 ppm by a hot press device while uniformly pressing the aluminum nitride substrate in the vertical direction. The joining material is Al-4.1% C
A foil having a u-0.5% Mg composition and a thickness of 10 μm was used. A resist ink is screen-printed so that a circuit pattern of a predetermined shape is formed on the aluminum circuit forming surface of the obtained joined body and a heat radiating plate pattern is formed on the heat radiating aluminum plate forming surface. Etching of the bonding layer, electroless Ni-P plating (thickness 3 μm)
Was performed to produce a circuit board. After that, thickness 0.8m
m, the tip of the tough pitch copper electrode terminal having a width of 2 to 2.5 mm was bent to obtain the bonding area shown in Table 1 and Table 2, and Table 1 was obtained by using “USW-610Z20S” manufactured by Ultrasonic Industry Co., Ltd.
Ultrasonic bonding was performed under the conditions shown in Table 2. AC50 was applied to the obtained circuit board with electrode terminals.
A dielectric breakdown test in which 00V was applied for 3 minutes was performed. Also,
After a thermal cycle test in which a temperature of −40 ° C. and a temperature of 125 ° C. were alternately performed 2000 times, a dielectric breakdown test in which AC 5000 V was applied for 3 minutes was performed. Furthermore, for the test piece that did not become defective, the circuit portion and the like were removed by chemical etching, and the horizontal crack rate around the circuit pattern was calculated by the formula:
(Length with horizontal crack) / (total length around circuit pattern). Tables 1 and 2 show these results.
Shown in [Table 1] [Table 2] As can be seen from Tables 1 and 2, the circuit board with electrode terminals manufactured according to the present invention does not have horizontal cracks in the substrate portion, such as aluminum nitride, immediately below the electrode terminals. It was found that it was enhanced and that it had a high insulation resistance. A test similar to the above was conducted using a silicon nitride substrate (size: 57 mm × 34 mm × 0.65 mm, bending strength: 700 MPa, thermal conductivity: 70 W / mK, purity: 92% or more) instead of the aluminum nitride substrate. As a result, the result was almost equivalent to the above. According to the present invention, a circuit board with electrode terminals having high insulation resistance can be manufactured with increased productivity without using solder.

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Claims (1)

Claims 1. A copper circuit formed by heating (a) a brazing material containing silver, copper, tin and zirconium in a nitrogen atmosphere on a ceramic substrate mainly composed of aluminum nitride or silicon nitride. Or joining a copper plate, or using (b) at least one kind of joining material selected from Al-Cu alloy foil powder, Al-Cu alloy foil powder, and a mixed powder containing Al and Cu, in a nitrogen atmosphere After the circuit or plate made of Al or Al alloy is joined by heating underneath, when a copper plate or a plate made of Al or Al alloy is joined, etching is performed to form the circuit, and the upper area of these circuits is reduced. At least one-third of the electrode terminal has an area of 3 to 30 mm ² for mounting one electrode terminal, and at least one of the electrode terminals has an output of 300 W or more, a frequency of 7 kHz or more, and an amplitude of 7 μm or more. A method for producing a circuit board with electrode terminals, characterized in that the circuit board is provided with lugi.